This is why we hear more and more stories about local and State governments making it illegal to film the police, and why the federal government has been doing the same for federal law enforcement:
The badge does not grant you immunity to the law. The police are just as accountable to the laws they enforce as those against whom they enforce them. This officer is guilty of assault and child abuse. He may also be guilty of crimes that apply to people in positions of higher authority/responsibility, such as police brutality. In a free and self-governing society, this guy gets charged, tried as any other perp would be and — no matter what the verdict — he is unemployed.
On the other hand, when the police are allowed to operate as though they are above the law, that is called tyranny, and tyranny invokes the natural right to self-defense.